Genotyping‐by‐sequencing analysis of Orobanche crenata populations in Algeria reveals genetic differentiation

Crenate broomrape (Orobanche crenata Forsk.) is a serious long‐standing parasitic weed problem in Algeria, mainly affecting legumes but also vegetable crops. Unresolved questions for parasitic weeds revolve around the extent to which these plants undergo local adaptation, especially with respect to host specialization, which would be expected to be a strong selective factor for obligate parasitic plants. In the present study, the genotyping‐by‐sequencing (GBS) approach was used to analyze genetic diversity and population structure of 10 Northern Algerian O. crenata populations with different geographical origins and host species (faba bean, pea, chickpea, carrot, and tomato). In total, 8004 high‐quality single‐nucleotide polymorphisms (5% missingness) were obtained and used across the study. Genetic diversity and relationships of 95 individuals from 10 populations were studied using model‐based ancestry analysis, principal components analysis, discriminant analysis of principal components, and phylogeny approaches. The genetic differentiation (F _ST) between pairs of populations was lower between adjacent populations and higher between geographically separated ones, but no support was found for isolation by distance. Further analyses identified four genetic clusters and revealed evidence of structuring among populations and, although confounded with location, among hosts. In the clearest example, O. crenata growing on pea had a SNP profile that was distinct from other host/location combinations. These results illustrate the importance and potential of GBS to reveal the dynamics of parasitic weed dispersal and population structure.     

Molecular phylogenetic analyses indicate a wide and ancient radiation of African hepatitis delta virus, suggesting a deltavirus genus of at least seven major clades

Hepatitis D virus (HDV) is a satellite of hepatitis B virus (HBV) for transmission and propagation and infects nearly 20 million people worldwide. The HDV genome is a compact circular single-stranded RNA genome with extensive intramolecular complementarity. Despite its different epidemiological and pathological patterns, the variability and geographical distribution of HDV are limited to three genotypes and two subtypes that have been characterized to date. Phylogenetic reconstructions based on the delta antigen gene and full-length genome sequence data show an extensive and probably ancient radiation of African lineages, suggesting that the genetic variability of HDV is much more complex than was previously thought, with evidence of additional clades. These results relate the geographic distribution of HDV more closely to the genetic variability of its helper HBV.     

A 3D Individual-Based Model to Study Effects of Chemotaxis,Competition and Diffusion on the Motile-Phytoplankton Aggregation

In this paper, we develop a 3D-individual-based model (IBM) to understand effect of various small-scale mechanisms in phytoplankton cells, on the cellular aggregation process. These mechanisms are: spatial interactions between cells due to their chemosensory abilities (chemotaxis), a molecular diffusion and a demographical process. The latter is considered as a branching process with a density-dependent death rate to take into account the local competition on resources. We implement the IBM and simulate various scenarios under real parameter values for phytoplankton cells. To quantify the effects of the different processes quoted above on the spatial and temporal distribution of phytoplankton, we used two spatial statistics: the Clark–Evans index and the group belonging percentage. Our simulation study highlights the role of the branching process with a weak-to-medium competition in reinforcing the aggregating structure that forms from attraction mechanisms (under suitable conditions for diffusion and attraction forces), and shows by contrast that aggregations cannot form when competition is high.     

Solvent effects of N‐nitroso,N‐(2‐chloroethyl), N′,N′‐dibenzylsulfamid and its copper(II) and cobalt(II) complexes: fluorescence studies

The structure of N‐nitroso, N‐(2‐chloroethyl), N′,N′‐dibenzylsulfamid (CENS) was established by X‐ray crystallography. The atomic coordinates, factors of isotropic thermal agitation, bond lengths and valence angles were determined. The solvent effects on the electronic absorption and fluorescence spectra of CENS were investigated at room temperature. The effects of solvent polarity and of hydrogen bonding were interpreted by means of linear solvation energy relationships (LSERs). Multiple linear regression analysis indicated that the hydrogen donation properties of the solvent play an important role in determining the position of the absorption maximum, while the classical polarity of the medium is the only dominating parameter in determining the emission maximum and the Stokes' shift. Complexation of the investigated compound by two different transition metal ions was studied. Fluorescence measurements show that fluorescence quenching by cobalt(II) is more important than that by copper(II). This phenomenon can be attributed to good stereo‐structural matching between the electronic configuration of the Co²⁺ ion and the active site distribution of CENS in aqueous solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Biocontrol of broomrape (Orobanche crenata Forsk. and Orobanche foetida Poir. ) by Pseudomonas fluorescens isolate Bf7-9 from the faba bean rhizosphere

Bacteria of the faba bean (Vicia faba L.)/Orobanche spp. root environment were evaluated for their potential use as biocontrol agents for the parasitic weed. Bacteria were isolated mainly from the rhizosphere of faba bean as well as from diseased Orobanche underground structures and an Orobanche-suppressive soil from three districts of northern Tunisia. Out of 351 bacterial isolates, 337 were tested for pathogenicity in an inverted pyramidal-shape screening programme including a Lactuca sativa L. seedlings bioassay, root-chamber and pot experiments. In pre-selection screening on L. sativa seedlings, 37 isolates (11%) showed a strong growth inhibitory effect, of which 70 and 84% also had a significant suppressive activity on the pre-emergence structures of O. foetida and O. crenata, respectively, in root-chamber experiments. Among five bacterial isolates selected for pot trials, strain Bf7-9 of Pseudomonas fluorescens showed high biocontrol activity against both species of Orobanche and positively influenced faba bean growth. The bacterium reduced shoot emergence of O. crenata and O. foetida by 64 and 76% and their dry weight by 39 and 63%, respectively, compared with non-inoculated controls. Pseudomonas marginalis strain Nc1-2 exhibited also a tendency to reduce incidence of O. crenata and to improve faba bean performance. Results of the present study suggest that application of naturally occurring rhizosphere bacteria offers an additional approach for biocontrol of Orobanche spp. that can supplement current methods of control in an integrated weed management strategy.     

Spectrofluorimetric determination of the antineoplastic agent lomustine based on the sensitizing effect of β‐cyclodextrin

The effects of solvent dipolarity/polarizability and solvent–solute hydrogen bonding on the photophysical properties of the antineoplastic drug lomustine were analysed by means of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft. The LSER method enabled the overall solvent effects to be quantitatively estimated and separated into specific and non‐specific contributions. The molecular encapsulation of lomustine by β‐cyclodextrin (β‐CD) has been studied using fluorescence spectroscopy. The results are discussed in terms of the binding parameter and the effect of the solvent used. It was concluded that β‐CD forms a 1:1 inclusional complex with lomustine in acetonitrile solution and its association constant was calculated to be 500 M^?1. In addition, and for the first time, a simple, rapid and high sensitive fluorimetric method for the determination of lomustine was developed based upon the enhancement effect produced through complex formation with β‐CD. The new approach for the quantification of lomustine in the presence of β‐CD was described in aqueous and organic solutions. Better limits of detection (0.31 µg ml^?1) and quantification (1.05 µg ml^?1) were obtained in aqueous solution with respect to those obtained in organic solvent. Copyright © 2015 John Wiley & Sons, Ltd.     

First report of Alternaria leaf spot caused by Alternaria alternata (Fries.) Kiessler on Sonchus oleraceus L. and Convolvulus arvensis L. in Algeria

Alternaria leaf spot caused by Alternaria alternata (Fries.) Kiessler was found on sow thistle (Sonchus oleraceus L.) and field bindweed (Convolvulus arvensis L.) in the experimental station of ENSA (Ecole Nationale Supérieure d'Agronomie) in Algiers, Algeria, during the winter of 2016. Necrotic spots in the form of concentric circles were observed on the leaves of both weeds with disease incidence of approximately 70% and disease severity ranging from 50% to 70%. Fungi were isolated from the infected leaves and identified as A. alternata, based on morphological and molecular analyses (using genetic marker internal transcribed spacer, ITS of rDNA). Pathogenicity tests confirmed that A. alternata is the causing agent of leaf spot disease of sow thistle and field bindweed in accordance with the original symptoms. To the best of our knowledge, this is the first report of sow thistle and field bindweed naturally infected by A. alternata in Algeria.     

On phytoplankton aggregation: a view from an IBM approach

In this paper, we build up an individual-based model (IBM) that describes the aggregative behavior in phytoplankton. The processes in play at the individual level (an individual=a phytoplankton cell) are: a random dispersal, a displacement due to the net effect of cells present in a suitable neighborhood (spatial interactions) and a branching (cell division and death). The IBM model provides a virtual world where phytoplankton cells appear to form clusters. Using this model, we explore the spatial structure of phytoplankton and present some numerical simulations that help the understanding of the aggregation phenomenon.